Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Process when painting car with urethane bumpers
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Old 07-24-2012, 07:46 PM
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Originally Posted by cyclopsblown34 View Post
Now that Brian has posted in here. What is your preferred procedure for repairing damage to these urethane bumpers? I had one years ago I fixed and the discolored area of the urethane shone through the paint like a beacon saying lookit what Chip screwed up. It's been so long ago, I cannot remember the procedure or materials I used.

some guys swear by plastic welding and some swear by plastic repair netting on the backside. Some people actually think heating up a screwdriver and remelting the plastic onto each other is welding...sort of, but the oils in the bumper will make it hard to adhere to each other and it will fail. Anyhow, the correct way is to locate the type of material it is inside the bumper cover. It will be a few letters like a paint code. Then you get the correct plastic rod and do a test on the backside to make sure it sticks well. Then you weld it. Most use hot air.

The correct way to net repair is to groove out the backside and frontside with a die grinder. Then throw tape in the hole you made bigger by grooving it out. Then add your plastic repair, then net, then more plastic repair. When it cures take the tape off and do the outside. Most people don't wait for it to cure and do both sides together.

Use flexible filler to top coat.

If you're working road rash than stick 80 grit on a da on it carefully. Then go over it with 180 for a long time to take the little fur balls out that collect when using 80 grit. Using 180-220 with the paper wet will get the fur balls out really fast. If you don't account for the fur balls you will be disappointed when you prime and see your wet primer so I'd never suggest 80 grit to someone who hasn't done many bumpers. Then use plastic repair if needed or a flexible filler . Some people use brown flexy crap that sands like junk instead of a flexible filler but I think it's junk and doesn't adhere well. Once you got the fur balls out you prep like anything else you'd spray but you spray a little adhesion promoter on bare plastic beforehand and add adhesion promoter to your primer, depending on what 2k you use. No need for adhesion promoter in your paint or clears anymore, or at least that's what is now guideline.
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